Plant for the production of oxygen



June 21, 1960 PLANT FOR THE PRODUCTION OF OXYGEN Filed Aug. 31, 1956 3Sheets-Sheet 1 FIG I I mmvrozc P. TuLAcz 2,941,375

June 21, 1960 P. TULACZ PLANT FOR THE PRODUCTION OF OXYGEN 3Sheets-Sheet 2 Filed Aug. 31, 1956 June 21, 1960 P.ITULACZ 2,941,375

PLANT FOR THE PRODUCTION OF OXYGEN Filed Aug. 31, 1956 3 Sheets-Sheet 3F INVENTOR.

\ r' [Mew- United States Patent PLANT FOR THE PRODUCTION OF OXYGEN PiotrTula'cz, Pueyrredon 2010, Bueuos Aires, Argentina Filed Aug. 31, 1956,Ser. No. 607,314

5 Claims. (Cl. 62-37) This invention relates to a plant for theproduction of oxygen and its final bottling.

The plant has been specially designed for putting advantageously inpractice the process of producing oxygen by fractionating the maincomponents of liquid airnamely, nitrogen and oxygenwith the eliminatlonof the carbon dioxide and humidity also present in liquid an.

The new assembly constituting the plant of the invention is acombination of elements, some of them already known, others completelynovel, assembled according to a certain functional order, placed andcorrelated so as to achieve an easy operation and to obtain and maintainthe two main factors which determine the final results. These factors,pressure and temperature, are balanced so as to obtain the highestbenefit by reciprocally increasing or decreasing one at the expense ofthe other; in this way, efiiciency is combined with economy inproduction costs and high quality of the oxygen obtained.

From the strictly constructive point of view, the plant of the inventionis constituted by the association of the following elements: means forthe admission and filtration of air combined with a first compressorwhich compresses the air up to a certain pressure and delivers it to asecond compressor, associated to the first one, wherein the pressure ofthe air rises to a higher level; the air so compressed passes through acarbon dioxide retaining device connected to a third compressor whichcompresses the air up to an even higher pressure. Directly following thethird compressor, there is connected a drier coupled to a first heatexchanger continued by a pipe which divides into two branches; of thesetwo branches, one is connected to a decompressor and to a second heatexchanger. The assembly includes a fractionating column, provided at itslower portion with a first coiled tube connected by one part of thebranch passing through the second heat exchanger and, by the other part,to a first column feeding pipe. The other branch of the branched pipe isconnected to a third heat exchanger and to the base of the said column,forming there a second coiled tube which, in its turn, is connected to asecond feeding pipe of the fractionating column. At the upper part ofthe fractionating column there is connected a third pipe which passesthrough the three heat exchangers and, finally, discharges to theatmosphere. The assembly is completed by a conduit which, starting fromthe said column at the zone adjacent to the coils, passes through thethird and first heat exchangers and is connected to a flow-control organassociated to a fourth compressor which is provided with means forbottling the oxygen into adequate recipients.

It must be remarked the important and novel fact that the decompressorand the third compressor have common crank and crankcase, thus beingavoidable the usual brake because the drive of the decompressor istransmitted directly to the crank. This arrangement results in a greateconomy in compressive work and also reduces the con struction costs.

It must be remarked also the particular construction and arrangement ofthe fractionating column which constitutes in itself one of the mostimportant organs ,of the plant of the invention.

With respect of the fractionating elements or trays of the fractionatingcolumn, it must be remarked the importance of achieving, the same as inthe case of a petroleum or alcohol rectifier, a maximum interchangebetween the liquid and gaseous phases in equilibrium.

With the usual dome or calotte, even in the case when the trays haveperipheral openings or are provided with a combshaped system of parallelteeth, the interchange between both liquid and gaseous phases isextremely brief, it being reduced to the very short lapse during whichthe vapor bubbles through the liquid covering the tray and sealing theedge of the dome. The case is similar with the Barbert, Savalle andYnillanme trays, though it must be reckoned that the Egrot tray isrelatively more eflficient in the case of rectifiers.

The multibored tray, such as used in the Savalle dis continuousrectifier, represents an important improvement, though the columnsprovided only with this type of fractionating element present theproblem of their too much easy discharge through the bores when the flowis lesser than that foreseen, this effect taking place normally when theplant starts to operate or when the temperature suddenly decreases in acertain zone of the column, particularly when the temperature of theliquid fed into the column changes.

The present invention solves this important aspect of thenitrogen-oxygen fractionating process by employing combined andsuperposed double trays with devices such that provoke an intensecirculation of the liquid'in the, lower tray, due to the effect of theissuing gases or vapors which impulse and circulate the said liquid and,simul-.' taneously, multiply, by repetition, the lapse during which bothphases are in contact, the said liquid finally dropping into the lowersystem as an overflowing foam through trop-pleins provided to such end.

In its turn, the base of this tray oifers, due to its concave shape, alarge surface of the gases coming up from the complementary lower tray,this fact having an important thermal influence on the liquid containedin the said tray.

The complementary tray is placed upon the afore mentioned tray and isprovided with bores all over its surface and is provided also withtrop-pleins for the discharge of liquid into the other tray, which willbe called from now on as the lower main tray. The interchange of phasesand calories takes place due to the passage of gases through the severaland small bores provided all over the surface of the upper element.

Discarding the effects of retrogradation from one tray to another andfrom one assembly to the immediate one, always present in fractionatingcolumns, it is re-' marked, in the case of this invention, the sinuouspath of the gas in its upward progress, since the gas strikes on thecentre of the middle portion of the lower tray, is then diverted to theperiphery, and from there passes, in a diffused way, to the upper unit,being directed there to the centre of the upper group.

The thorough, multiple and persistent interchange between the liquid andgaseous phases, and the rupture in the uniformity of the ascending flow,due to the sinuous direction of its path, result in an intenserectification or fractionation, the ascending nitrogen gases beingextraordinarily enriched as they lose oxygen, and the latter, in itsturn, progressively deprived of nitrogen as it falls or retrogrades as aliquid phase from one tray to another. The chance of a probabledischarge of the bored tray in the case of depressions produced byexcessive condensation at certain zones is prevented and solved in thetray" of each group which is filled with liquid and, as

the latter makes a water or hydraulic seal over the whole surface of.the tray, the normal dischargepath of the liquid through the troppleins, thus being discarded the possibility of a direct communicationbetween groups.

This is particularly important when the column starts to operate,because thedistillation ta'kes'place at the desired rate and in a timeshorter than that needed in the normal operation with uniform trays.

Equally remarkable among the organs constituting the plant of theinvention is the organfor controlling the volume of liqu'idflowi'ng intothe compressor of the bottl ing machine. The said organ, which. will becalled state-volume, tends to maintain a steady provision of oxygen forthe compressor of the bottling machine, in order that under nocircumstance the said compressor would draw directly from the circuitbecause in that case a harmful altera-' ti'on'iifthe pressure regimen atthe intake zone and, consequently, in the fractionating column, takesplace when the feeding rate of the bottling machine is greater than,

the production rate of the plant.

Up to the present there were not eflicient and practical means forpreventing this trouble. The present invention solvesv this problem in anovel and satisfactory way by the employment of a rubber bag placedinside a metallic tank, the upper portion of the said bag beingconnected by means of two fixed pipes to the intake of thecompressor'and to the circuit carrying. pure oxygen. A relatively heavybody rests on the upper portion of the bag and. has arms for the commandof sin-electric switch constituted by a cell partially filled withmercury.

The cell has two electric wires connected to the eleccir'cuit operatingthe compressor and placed in such way that, when the bag is empty, thecell adopts, as an of the movement of the arms, a positionin which. themercury covers only one of the electric wires, at.

most; When thebag is almost filled the cell adopts a pdsition'in whichthe mercury covers both wires, thus closing the electric circuit whichoperates the compressor which is drawing the oxygen out of the bag. andimpulsing it into the bottle. A similar performance would be achieved bymeans of an electromagnetic valve operating the intakev valve of thecompressor.

Two stop members, placed on the upper arm, de-' termine, due to theircomplementary action on a forked lever operating on a switch, the momentat. which the circuit is closedor opened. a

It is. particularly important, due to its novel characteristics, thecontrollable air decompressor which tends to. produce. a. decompressionin the pre-cooled air so as to obtain, by expansion, :1 better coolingeffect. To mainthe, required air temperature and pressure rates afterthe decompression implies the compensation of, the variations in thesystem duev to the fluctuating thermal conditions of the external airfed into the circuit.

The preceding aim has beenfrequently approached by applying variableresistances in the electric circuit, by

braking themotor, etc., in order to regulate the number of revolutions.per. minute of the decompresson thusresultin-the latter an increased ordecreased number of strokes per minute. I

The, present inventionolfers a novel, efiicient and practical solutionof the problem presented by the fluctuating air conditions.

This solution is based on the existing correlation be tween the fall inthe air temperature, which is the phenomenon. desired, and the airpressures before and after the said fall of temperature, due to thedecompression of the volume of air introduced into. the cylinder of thedecompressor. This is achieved by modifying the volume ofv the aireffectively introduced by regulating the moment oflclosing the intakevalve of the decompressor in rela- 4 tion to the moment when the pistonis at the top dea center and, correlatively, by regulating the moment ofopening the exhaust valve. To a greater retard in closing the admission,corresponds a greater volume of intake air. In its turn, the greater isthe volume of the air introduced, the greater is, for the same cylindercapacity, the cooling effect and correlatively. I

In the case of the plant-for the production of oxygen which is theobject of this invention, the regimen must be obtained by means of adecompression from 40 to 5 atmospheres; these being the normal pressuresbefore. and after the said decompression.

In the accompanying drawings 1 Fig. 1 represents schematically the plantfor the production of oxygen and its final bottling.

Fig. 2 illustrates a vertical cross-section of the fractionating column,showing the constructive details of the component trays.

Figs. 3 and 4 are top views showing the characteristics of the elementsconstituting the column.

Figs. 5, 6 and 7, represent, respectively, twolateral and a top view ofthe organs for controlling the volume of oxygen flowing into thecompressor of the bottling m'achine. Fig. 5 is-taken along line of AA ofFig. 7 and- Fi'g. 6 is taken along line- BB' of Fig. 7.

Figs. 8 and 9 represent different aspects of the decompressor regulatingdevice, Fig. 10 being a variant of the same device.

According to what is illustrated in Fig. l, the plant of the inventioncomprises means,- related to compressors- Z and '3, for the admissionand filtering of the air, the first and second compression stages takingplace inside those compressors.

The column -4' is a carbon dioxide retaining device- The air, filteredat 1, is first compressed up to 3 atmos pheres (about 45' pounds persquare inch) in the compressor 2, then passes to the compressor 3wherein its" pressure is increased up to 12 atmospheres (about 1pounds). The airthen ascends through the column 4, leaving there itscarbon dioxide content, and then passes to the compressor 5 wherein iscompressed for the third, time up toa pressure of 4042 atmospheres(about 600 pounds).

Then, the -air descends through the drier 6 and ascends through the heatexchanger 7, where its temperature is reduced to C. below zero, andthrough the pipe 9 branched off in two pipes, 15 and 15a. carries offthe larger amount of air, and is connected to the decompressor 10wherein the said air expands while its pressure is reduced down to 4' or5 atmospheres (about 60-70 pounds), and due to this decompression thetemperature of the air is lowered to C. below zero. From there, the airflows through the pipe 11 into the heat exchanger 12 wherein itstemperature drops to C. below zero due to the refrigerating effect ofthe very cool nitrogen coming, as it will be explained later on, fromthe column 13, and ascending through the said heat exchanger.

The semi-liquified air flows inside the cooling coil 14.

at the base of the fractionating column 13, the said coiltionating toweror column 13, at the upper portionof the latter.

The branch 15' The other branch a derived from the pipe 9 is connectedto the heat exchanger 16. The air flowing inside of it is cooled down to142 C. below zero due to the combined effect of the counter-currentrefrigeration by the oxygen flowing inside a coil and of the nitrogenfed through the pipe 17 and diffused inside the said heat exchanger. Thesaid air flows inside the pipe 18 and enters the fractionating column atthe base, wherein it is cooled and liquified as it passes through acoil, and is fed from above into the fractionating column 13 afterpassing through the pipe 19 and the throttle valve 20'.

The fractionating column, 13, partially represented in Fig. 2, isconstituted by a series of superposed trays 22, particularly illustratedin Figs. 2, 3 and 4 (22 and 22a).

The tray 22 is constituted by a disc 30 whose periphery abuts againstthe wall of the column 13. The said disc is provided with regularlyspaced bores 38 of 2 millimeters in diameter. The tubular trop-pleins 31overtop the trays up to a certain height corresponding to the level theliquid should reach when covering the tray, the said tray oifering ametallic concavity 32 which makes easier the discharge of the exceedingliquid towards the main trop-plein 33 in the lower or main tray 22a.This lower or main tray consists of a container whose circumferentialperiphery coincides and is adjusted to the wall of the column 13, thesaid container being constituted by a plate with a concave bottom at itscentral zone, a straight portion 35 inclined towards the periphery 36,and a circular recess 37 at the centre of the tray, this recess limitingthe storage capacity of the tray.

The tube 33, provided with a funnel 39, a fold 40- and a flange 41,rests on the central recess 37 of the tray, its flange 41 offering abearing edge for the annular plate 42, whose surface is corrugated atsharp angles, the said plate being placed as an inverted shell with acentral opening 43. The corrugated annular plate 42 rests along itsperiphery on the lower tray, and maintains a certain clearance withrespect to the wall of the periphery 36 of the said tray.

The lower end of the trop-plein 33 is inserted into the concavity 32 ofthe bored tray which, together with another unit 22a, constitutesanother double tray of the plurality of similar assemblies constitutingthe fractionating column 13.

Generally speaking, the process inside the fractionating column is asfollows:

The liquid air drops from one tray into another while being submitted tothe countercurrent of vapors or gases, particularly rich in nitrogen,issued as the liquid air descends the column, pure oxygen being thusobtained, finally, at the base of the column. The nitrogen, as a gaseousphase, is progressively deprived of oxygen as it mounts the tower orcolumn and, at the end of this process comes out with a 10% content ofoxygen. This nitrogen is taken by the pipe 23 and carried through theheat exchangers 12, 16 and 7, being finally delivered to the atmosphereafter passing through the regulating valve 25.

The gaseous oxygen separated by effect of the heat exchanged at thecoils 14 and 18 at the base of the column comes out from 24 as asaturated gas, passes through the heat exchangers 16 and 7 and throughthe valve 26, and flows then to the compressor 27, after passing throughthe stato-volume 28, being finally bottledinto the tube 29.

1 Particularly considered, the operation inside each combined tray 22and 22a is as follows (Fig. 2):

, The sinuous line 45 and the branches derived from it represent theascendent path of the gases through one section of the column, and thelines 46 represent the flow of the liquid phase as it overflows anddrops into the lower combined tray. The line 47 illustrates the firmrecirculation of clean liquid under the pressure of the gases. Thisprocess is reproduced in an identical way in each one of the sections orcorrugations of the annular plate 42, thus putting into evidence theintense exchange between the liquid-gaseous phases of theoxygen-nitrogen as the oxygen descends the column and is progressivelypurified.

In this way, due to the novel characteristics of the fractionatingcolumn and the intense exchange obtained in its double trays, it ispossible to obtain an oxygen of maximum purity with a minimum of trays.

In Figs. 5, 6 and 7, the organ for controlling the volume of oxygendrawn in by the compressor of the bottling assembly is represented indetail.

This controlling organ, which has been referred to in this descriptionas the stato-volume, is constituted by a metallic box 48 provided with alid 58, inside of which there is placed a rubber bag 49.

A heavy body 53 rests upon the upper portion of the said bag, the saidbody having a metallic arm 59 rotatingly mounted at 52, between thepipes 50 and 51, or at other fixed portion such as the lid 58.

A second metallic arm 54, of an easy-curved shape, is fixed to the body53, forming an angle of about with respect to the arm 59, passes freelythrough the opening 60 in the lid 58, and ends at 61.

The arm 54 operates the cell of a mercury electric switch 57.

It is a characteristic of the invention the fact that two stop members,put at a certain distance at the upper part of the arm 54, act upon aforked member operating in an electrical switch placed so as to causethe operation of the said forked member as the arm 54 moves upwards ordownwards, the said switch and forked member being fixed to a pointindependent of the said arm.

The state-volume operates in the following way:

The bag 49 being empty and the cell being at the position shown in Fig.6, the compression does not take place due to the fact that the electriccircuit remains open as long as the mercury is accumulated at one end ofthe cell. The gaseous oxygen flows into the bag through the pipe 50,under the effect of the gas pressure inside the piping system of theplant. As the bag 49 gets filled with oxygen, the said cell tends toadopt a horizontal position up to .the point where the mercury touchesboth ends of the cell and thus closes the electric circuit; at this verymoment, the compressor 27 starts to operate, Fig. 1, continuouslydrawing in oxygen through the pipe 51 and compressing it into the tubeor bottle 29 (Fig. 1) until the bag is emptied; at this moment theelectric switch is opened and, consequently, the compressor stops.

The application of the eletcric switch and its corresponding fork, notrepresented in the drawings, makes possible to regulate the opening ofthe circuit at any determined position of the arm 54.

The controllable decompressor 19, Figs. 8 and 9, is constituted by aplunger 61 pushed by a connecting rod of the corresponding compressorrunning at a fixed number of revolutions per minute, the cylinder 62being sealed by means of the packings 63, 64 and 65, the intake andexhaust valves being respectively operated by the levers 66 and 67, theearns 68 and 69 being moved, in their turn, by the camshaft 70.

The said camshaft and the cams have an elongated helicoidal key 71mounted in a groove of similar shape formed in the said camshaft.

' The fork 75 embraces both cams and is apt to be moved along thecamshaft due to the action of a worm 78 sup ported by bearings 77 fixedto the base of the housing, the said worm being operated by the crank'79.

The operation is as follows:

If the volume of the intake air is to be reduced, the fork 75 and,consequently, the cams 68 and 69 must move along the camshaft impulse bythe crank 79 and worm 78 mechanism; the displacement of the forkproduces, due to the helicoidal key 7-1, a revolving movement of the camwith respect to the camshaft, and the resulting angle of rotationdetermines the moment when the cam oper.

ates upon the" intake valve, in relation to the intake stroke of' theplunger whose driving "axle'is synchronized with the camshaft, 'as'usual.

In the present invention, the air normally fed into the deeoin ressor isat 40 atmospheres andmust be decompressed down to atmospheresand 150 C;below zero, these being the normal operating: conditions or the rest Ofthe plant. Th external all temperature VQIidtiOHS particularly afiectthepressure and temperature of the air fed into the deeompfessor; In the;ease of this invention, the regulation of these conditionscan beachieved even when the plant is fully o erating 1 It has been alsoforeseen the independent application of the device of the invention toeach cam, in order to adjust the closing of the intake valveindependently from ii'l opening Of'ih'o exhaust Valv; 4 V

" Another solutioriof this important problem is that illusti'fited inFig. 10. l Y a The camshaft 70 has a pinion 74-, and there is providedanother pinion 72 fixed to the com ressor camshaft, both pinions beingengaged by the chain 73. A lever 81,opersting of: the camshaft 70',has-an"- adjustable and movable pinion 80, also engaged to the chain'73'i' Finally-,- there is a tension pinion 82 also engaging the saidchain.

The operation of this latter device is as follows: 7

If, when the camshaft and the compressor crankshaft are-normallsynchronized, the pinion 80 is displaced by means of the lever 81 sothat the chain engages the pinion 74 along an increased circumferentiallength corresponding to the angle b, a similar but opposed anddiminished effect takes'pl'ace at the crankshaft pinion. The relativemovement of the camshaft with respect to the pinion of the crankshaft isthus retarded, this retard being transmitted to the opening and closingoperation of the valves.

Having described the invention and the way of its prac-- ticalexecution, it is claimed as exclusive property and right:

1. In an apparatus for producing oxygen from air by at least partialliquefaction of said a'ir'and fractiona tion thereof at predeterminedpressure in a fractionati'ng vessel, in' combination, movableoompressor'means for compressing air to be liquefied; expander means forexpandi'ng a controlled portion" of said compressed air, said expandermeans being connected to said compressor means for joint movement,adjustable control-'meansfor controlling the amount of air to beexpanded in said c'x pander means duringmove'ment thereof with saidcompressor means; conduits for respectively feeding said expandedportion of said compressed air and the remaining portion thereof inuncxpandcd condition to said fractionating vessel; withdrawing means forwithdrawing oxygen from said fractionating vessel through a dischargeconduit and including a collapsible storage means sensitive to thepressure in said conduit; and pressure'responsive'control meansresponsive to pressure variation in said discharge conduit forcontrolling the rate of withdrawal of said oxygen from saidfractionating vessel and including ac-- tuating means associated withsaid storage means for actuating operation of said withdrawing means soas to actuate said withdrawing means when said sto'r'ag'emcans is in thenon-collapsed condition and stopping operation of said withdrawing meanswhen said storage means is 'in a collapsed condition, whereby thepressure in "said fracti'onating'vessel is maintained at apredeterminedvalue.

2. Inan apparatus for producing oxygen from air by at least partialliquefaction of said airahdfractionation thereof at predeterminedpressure in' a fractioh'a'ting' vessel, in combination, movablecompressor niean's'for coinprcssing air to be liquefied; expander meansfor expanding a controlled portion of said compressed air, said expandermeans being connected to said-compressor means for joint movement;adjustable control means forcohtrolling the amount of air'tobeexpandcdin said expander mean during movement thereof with saidcompressor means;conduits for respectively feeding saidexpanded portion of saidcompressed air and the remaining portion thereof in unexpanded conditionto said fiactio'nating vessel; withdrawing means for withdrawing-oxygenfrom said fractionating vessel through a discharge coliduit andincluding a collapsible storage means' sensitive tothe pressure in saidconduit; and pressure responsive control means responsive to pressurevariation in said discharge conduit for controllingthe ratc ofwithdrawal of saidoxygen from said fractionating vessel and'includ ingactuating means associated with said storage means for actuating"operation of said withdrawing meansso as to actuate said withdrawingmeans when said storage means is in the non-collapsed condition andstopping operation of said withdrawing meanswhen saidsto'rage means isin a collapsed condition, said actuating means comprising a liquidswitch of the type thatthe switch; is in the on position when the liquidin the switch touches two contacts at opposite ends of a level-likecontainer, said switch being associated with the top of said collapsiblestorage means, thereby actuating said withdrawing means when saidstorage means is substantially full 'a n'd the switch is level, andstopping the operation of withdrawing means when said storage meanshavecollapsed sufficiently for the relative level position of the switch tohave shifted so that the switch liquid no longer covers the contacts,whereby the pressure in said frat? tionating vessel is maintained at apredetermined value.

3. In an apparatus for producing oxygen from by at least partialliquefaction of said air and fractionation thereof at predeterminedpressure in a fractionatin'g ves sel, in combination,movable'comp'ressor meansfor'compressing air to be liquefied; expandermeans for expanding" a controlled portion of said compressed air,said-*expander means being connected to said compressor'mea'ns for jointmovement; adjustable control means for con-- trolling the amount of airto be expanded in said expander means during movement thereof with saidoompre's'so'r means, including intake and output valve meansand'actuating means for actuating the opening andclos ing' of said valvemeans in a predetermined time cycle in unison with movement of saidexpander means and including a pair of eccentric cams, one of saidJca'msbeing designed to operate the intake valve means of said expander means,the other of said cams beingldsifled' to operate the output valve meansof said expander means, acamshaft synchronously movablewith'sa'idexpander means onwhich camshaft said cams aremount'ed, andmanual means to vary" the angular positionof 's'a'id' cams on saidshaft, whereby the relativepositionofthe expander means and therespective valv'e'm'ea'ns is varied", conduits for respectively feedingsaid expanded portion of-said' compressed air and the remaining portionthereof in unexpandcd condition to said fractionating vessehwith drawingmeansfor withdrawing oxygen from said fractionating vessel throughadischarge conduit; andpressu-re' tained at a'predetermined value.

4. In an apparatus for producing oxygen from by at least partialliquefaction of said air and fractionation thereof at predeterminedpressure in afractionati'ng'ves sel, in'cornbination, movable compressornieans ror'edmprcssingair to be liquified; expander means'for xpaiidirfga controlled portion of said compressed air, said expander means beingconnected to said compressor moaiis' -for joint movement; adjustablecontrol means for controllingthe amount ofair to'be expanded in saidexpander means during movement thereof with-said compressor-means,

including intake and output valve means, actuating-meansfor actuatingthe opening and closingvof said valve means in apred'et'errninedtimecycle in'unison-with movement of s agtd ex ander means, atpairofeccentric'camsoneot said cams being designed to operate the intakevalve means of said expander means, the other of said cams beingdesigned to operate the output valve means of said expander means, acamshaft synchronously movable with said expander means on whichcamshaft said cams are mounted, a helical key on said camshaft engagingsaid cams, holding means holding said cams in a predeterminedrelationship, and a manually rotatable worm, the rotation of which movessaid holding means and therefore said cams along the camshaft, theangular position of said cams relative to said camshaft being varied bysaid helical key while said cams move along said camshaft, whereby therelative position of the expander means and the respective valve meansis varied; conduits for respectively feeding said expanded portion ofsaid compressed air and the remaining portion thereof in unexpandedcondition to a said fractionating vessel; withdrawing means forwithdrawing oxygen from said fractionating vessel through a dischargeconduit; and pressure responsive control means responsive to pressurevariation in said discharge conduit for controlling the rate ofwithdrawal of said oxygen from said fractionating vessel, whereby thepressure in said fractionating vessel is maintained at a predeterminedvalue.

5. In an apparatus for producing oxygen from air by at least partialliquefaction of said air and fractionation thereof at predeterminedpressure in a fractionat-ing vessel, in combination, movable compressormeans for compressing air to be liquefied; expander means for expandinga controlled portion of said compressed air, said expander means beingconnected to said compressor means for joint movement; adjustablecontrol means for controlling the amount .of air to be expanded in saidexpander means during movement thereof with said compressor means,including intake and output valve means, actuating means for actuatingthe opening and closing of said valve means in a predetermined timecycle in unison with movement of said expander means, a pair ofeccentric cams, one of said cams being designed to operate the intakevalve means of said expander means, the other of said earns beingdesigned to operate the output valve means of said expander means; acamshaft synchronously movable with said expander means on whichcamshaft said cams are mounted, rotary driving means for driving saidexpander means, a sprocket and chain arrangement connecting said cams tosaid driving means for synchronous operation, said chain having a tightand a slack strand, and an adjustable sprocket acting on said chain tovary the relative lengths of said tight and slack strands so that therelative angular position of said cams and said drive means duringsynchronous movement thereof may be controlled; conduits forrespectively feeding said expanding portion of said compressed air andthe remaining portion thereof in unexpanded condition to a saidfractionating vessel; withdrawing means for withdrawing oxygen from saidfractionating vessel through a discharge conduit, and pressureresponsive control means responsive to pressure variation in saiddischarge conduit for controlling the rate of withdrawal of said oxygenfrom said fractionating vessel, whereby the pressure in saidfractionating vessel is maintained at .a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS1,917,891 Levin July 11, 1933 1,956,495 De Baufre Apr. 24, 19342,678,541 Sheen May 18, 1954 2,685,174 Collins Aug. 3, 1954 2,685,179Paget Aug. 3, 1954 2,701,710 Schilling Feb. 8, 1955 2,702,696 PappasFeb. 22, 1955 2,709,348 Yendall May 31, 1955 2,715,316 Paget Aug. 16,1955 2,732,692 Collins Jan. 31, 1956 2,763,137 Collins Sept. 18, 19562,772,543 Berry Dec. 4, 1956

